1. Field of the Invention
The invention relates to a liquid crystal display device, and more particularly, to an array substrate for an in-plane switching mode liquid crystal display device and a fabricating method of the same.
2. Discussion of the Related Art
Generally, a liquid crystal display (LCD) device uses optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite alignment direction as a result of their thin and long shapes. The alignment direction of the liquid crystal molecules can be controlled by applying an electric field across the liquid crystal molecules. In other words, as the intensity or direction of the electric field is changed, the alignment of the liquid crystal molecules also changes. Since incident light is refracted based on the orientation of the liquid crystal molecules due to the optical anisotropy of the liquid crystal molecules, images can be displayed by controlling the light transmittance of the liquid crystal material.
Since the LCD device including thin film transistors as a switching element, referred to as an active matrix LCD (AM-LCD) device, has excellent characteristics of high resolution and displaying moving images, the AM-LCD device has been widely used.
The AM-LCD device includes an array substrate, a color filter substrate and a liquid crystal layer interposed therebetween. The array substrate may include a pixel electrode and thin film transistor, and the color filter substrate may include a color filter layer and a common electrode. The AM-LCD device is driven by an electric field between the pixel electrode and the common electrode to have excellent properties of transmittance and aperture ratio. However, since the AM-LCD device uses a vertical electric field that is perpendicular to the substrates, the AM-LCD device has poor viewing angles.
An in-plane switching (IPS) mode LCD device has been suggested and developed to resolve the above-mentioned limitations.
FIG. 1 is a cross-sectional view of a related art IPS mode LCD device. As shown in FIG. 1, the related art IPS mode LCD device includes an upper substrate 9 and a lower substrate 10 spaced apart from and facing each other. A liquid crystal layer 11 is interposed between the upper and lower substrates 9 and 10. A common electrode 17 and a pixel electrode 30 are formed on the lower substrate 10. The common electrode 17 and the pixel electrode 30 may be disposed on the same level. Liquid crystal molecules of the liquid crystal layer 11 are driven by a horizontal electric field L is induced between the common and pixel electrodes 17 and 30. Although not shown in the figure, a color filter layer is formed on the upper substrate 9. The lower substrate 10 including the common electrode 17 and the pixel electrode 30 may be referred to as an array substrate. The upper substrate 9 including the color filter layer may be referred to as a color filter layer.
FIGS. 2A and 2B are cross-sectional views showing turned on/off conditions, respectively, of a related art IPS mode LCD device. As shown in FIG. 2A, when the voltage is applied to the IPS mode LCD device, arrangement of liquid crystal molecules 11a above the common electrode 17 and the pixel electrode 30 is unchanged. However, liquid crystal molecules 11b between the common electrode 17 and the pixel electrode 30 are horizontally arranged due to the horizontal electric field L. Since the liquid crystal molecules 11b are arranged by the horizontal electric field L, the IPS mode LCD device has a characteristic of a wide viewing angle. For example, the IPS mode LCD device has a viewing angle of about 80 degrees to about 85 degrees up and down and right and left without an image inversion or a color inversion.
FIG. 2B shows a condition when the voltage is not applied to the IPS mode LCD device. Because an electric field is not induced between the common and pixel electrodes 17 and 30, the arrangement of liquid crystal molecules 11 is not changed.
FIG. 3 is a plan view illustrating a portion of an array substrate for a related art IPS mode LCD device. In FIG. 3, the array substrate 40 includes a gate line 43, a common line 47, a data line 60, a plurality of common electrodes 49a and 49b, a plurality of pixel electrodes 70 and a thin film transistor Tr. The gate line 43 extends along a first direction, and the common line 47 is parallel to the gate line 43. The data line 60 extends along a second direction perpendicular to the first direction to cross the gate line 43 and the common line 47. Particularly, a pixel region P is defined by a crossing of the gate and data lines 43 and 60.
The thin film transistor Tr is disposed at a crossing portion of the gate and data lines 43 and 60. The thin film transistor Tr includes a gate electrode 45, a semiconductor layer 50, a source electrode 53 and a drain electrode 55. The source electrode 53 extends from the data line 60, and the gate electrode 45 extends from the gate line 43. The pixel electrodes 70 are connected to the drain electrode 55 through a drain contact hole 67 and disposed in the pixel region P. The common electrodes 49a and 49b are alternately arranged with the pixel electrodes 70 and extend from the common line 47.
The common electrodes include first common electrodes 49a and a second common electrode 49b. The second common electrode 49b is disposed between the first common electrodes 49a, and each of the first common electrodes 49a is disposed adjacently to the data line 60. In this case, each first common electrode 49a is spaced apart from the data line 60 with a predetermined distance. A common voltage is applied to the common electrodes 49a and 49b through the common line 47, which is horizontally across the pixel region P in the context of the figure, and an additional compensation or tuning for a difference in a common voltage resulted from charging of a constant voltage is required. Accordingly, production costs increase and a fabricating process is complicated.
In addition, the first common electrodes 49a is spaced apart from the data line 60 to prevent signal interference between the first common electrodes 49a and the data line 60, and the pixel electrodes 70 and the second common electrode 49b are alternately arranged. Therefore, an aperture ratio of the IPS mode LCD device decreases.